stepcompress: Always return 0 on negative number in safe_sqrt()

sqrt() of a negative number in the C code returns NaN.  This value
results in behavior that is difficult to debug.  Always return 0.0
instead as this results in better behavior that is easier to track
down.  Also, on some code paths, safe_sqrt is called on numbers that
are multiplied by very large amounts (eg, 16000000**2) and thus
distinguishing between large and small negative numbers is difficult.
For now, report in the log if the value is below -0.001.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 5 insertions, 5 deletions

diff --git a/klippy/stepcompress.c b/klippy/stepcompress.c
index 962039cd..a139a1f1 100644
--- a/klippy/stepcompress.c
+++ b/klippy/stepcompress.c
@@ -281,11 +281,11 @@ check_line(struct stepcompress *sc, struct step_move move)
 static double
 _safe_sqrt(double v)
 {
-    if (v > -0.001)
-        // Due to floating point truncation, it's possible to get a
-        // small negative number - treat it as zero.
-        return 0.;
-    return sqrt(v);
+    // Due to floating point truncation, it's possible to get a small
+    // negative number - treat it as zero.
+    if (v < -0.001)
+        errorf("safe_sqrt of %.9f", v);
+    return 0.;
 }
 static inline double safe_sqrt(double v) {
     return likely(v >= 0.) ? sqrt(v) : _safe_sqrt(v);